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Abstract:

Regarding a boundary acoustic wave device in which at least a part of an
IDT electrode is embedded in a groove disposed in a piezoelectric
substrate, the acoustic velocity is increased. A boundary acoustic wave
device is provided with a piezoelectric substrate, a first dielectric
layer, and an IDT electrode. The surface of the piezoelectric substrate
is provided with a groove. The IDT electrode is disposed at the boundary
between the piezoelectric substrate and the first dielectric layer in
such a way that at least a part thereof is located in the groove. In the
inside of the groove, the groove angle γ, which is the size of an
angle formed by an upper end portion of the inside surface of the groove
with the surface of the piezoelectric substrate, is less than 90 degrees.

2. The boundary acoustic wave device according to claim 1, further
comprising a second dielectric layer which is disposed on the first
dielectric layer and which has an acoustic velocity larger than that of
the first dielectric layer.

3. The boundary acoustic wave device according to claim 2, wherein each
of the first and the second dielectric layers is made of silicon oxide,
silicon nitride, or aluminum nitride.

4. The boundary acoustic wave device according to claim 1, wherein an
average density of the first portion of the IDT electrode is higher than
an average density of the piezoelectric substrate.

5. The boundary acoustic wave device according to claim 1, wherein at
least a portion of the first portion of the IDT electrode is made of at
least one metal selected from the group consisting of Pt, Au, W, Ta, Mo,
Ni, and Cu or an alloy containing at least one metal selected from the
group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu.

6. The boundary acoustic wave device according to claim 1, wherein the
IDT electrode includes a laminate including a plurality of electrode
layers, and a resistivity of at least one layer of the plurality of
electrode layers is about 5 μΩcm or less.

7. The boundary acoustic wave device according to claim 7, wherein the
electrode layer having a resistivity of about 5 μΩcm or less is
made of at least one metal selected from the group consisting of Al, Cu,
Au, and Ag or an alloy containing at least one metal selected from the
group consisting of Al, Cu, Au, and Ag.

8. The boundary acoustic wave device according to claim 1, wherein the
IDT electrode includes a laminate including a plurality of electrode
layers, and a diffusion preventing film is disposed in at least one of a
location between the IDT electrode and a bottom of the groove and a
location between adjacent electrode layers of the plurality of electrode
layers.

9. The boundary acoustic wave device according to claim 8, wherein the
diffusion preventing film is made of at least one metal selected from the
group consisting of Ti, Ni, Cr, and Ta or an alloy containing at least
one metal selected from the group consisting of Ti, Ni, Cr, and Ta.

10. The boundary acoustic wave device according to claim 1, wherein the
groove angle is within the range of about 10.degree. to about 80.degree..

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a boundary acoustic wave device
for use as a resonator and a filter device, for example. In particular,
the present invention relates to a boundary acoustic wave device in which
at least a portion of an IDT electrode is embedded in a groove disposed
in a piezoelectric substrate.

[0003] 2. Description of the Related Art

[0004] The boundary acoustic wave device is an elastic wave device which
does not require a package having a cavity and which can be miniaturized
as compared with a surface acoustic wave device. Therefore, the boundary
acoustic wave device has attracted rising attention in recent years.

[0005] For example, WO 2008/044411 A1 described below discloses a boundary
acoustic wave device in which at least a portion of an IDT electrode is
embedded in a groove disposed in a piezoelectric substrate. FIG. 78 is a
magnified schematic cross-sectional view showing a portion of an IDT
electrode of this boundary acoustic wave device. As shown in FIG. 78, a
boundary acoustic wave device 101 is provided with a LiNbO3
substrate 102. A silicon oxide film 103 is disposed on the LiNbO3
substrate 102. An IDT electrode 104 is disposed at the boundary between
the LiNbO3 substrate 102 and the silicon oxide film 103. The IDT
electrode 104 is embedded in a groove 102a disposed in the LiNbO3
substrate 102. The upper surface of the IDT electrode 104 must be flush
with the surface of the LiNbO3 substrate 102.

[0006] WO 2008/044411 A1 discloses that the upper surface of the IDT
electrode 104 must be flush with the surface of the LiNbO3 substrate
102, the upper surface of the silicon oxide film 103 is flat and,
thereby, a low insertion loss can be realized.

[0007] However, regarding the boundary acoustic wave device 101 in which
the IDT electrode 104 is embedded in the groove 102a of the LiNbO3
substrate 102, there is a problem in that the acoustic velocity of
propagating boundary acoustic wave cannot be increased sufficiently.

SUMMARY OF THE INVENTION

[0008] In consideration of such circumstances, preferred embodiments of
the present invention increase an acoustic velocity of a boundary
acoustic wave device in which at least a portion of an IDT electrode is
embedded in a groove disposed in a piezoelectric substrate.

[0009] A boundary acoustic wave device according to a preferred embodiment
of the present invention includes a piezoelectric substrate, a first
dielectric layer, and an IDT electrode. A surface of the piezoelectric
substrate is provided with a groove. The first dielectric layer is
disposed on the surface of the piezoelectric substrate. The IDT electrode
is disposed at a boundary between the piezoelectric substrate and the
first dielectric layer in such a way that at least a portion thereof is
located in the groove. Inside of the groove, a groove angle, which is the
size of an angle defined by an upper end portion of an inside surface of
the groove with the surface of the piezoelectric substrate, is less than
about 90 degrees, for example.

[0010] In the present specification, it is defined that the surface of the
piezoelectric substrate does not include the bottom surface and the side
surface of the groove.

[0011] In a preferred embodiment of the present invention, a portion of
the IDT electrode is located outside the groove, and the portion of the
IDT electrode located outside the groove is tapered so as to decrease in
size moving away from the piezoelectric substrate. Regarding this
configuration, it becomes difficult to form a gap between the first
dielectric layer and the IDT electrode and, therefore, degradation in
filter characteristic and resonant characteristic can be prevented.

[0012] In another preferred embodiment of the present invention, the
boundary acoustic wave device is further provided with a second
dielectric layer which is disposed on the first dielectric layer and
which has an acoustic velocity larger than that of the first dielectric
layer. A boundary acoustic wave is confined in the first dielectric layer
effectively by disposing the second dielectric layer. Therefore, the
insertion loss can be reduced because of a waveguide effect.

[0013] In another preferred embodiment of the present invention, each of
the first and the second dielectric layers is preferably made of silicon
oxide, silicon nitride, or aluminum nitride, for example.

[0014] In another preferred embodiment of the present invention, the
average density of the portion of the IDT electrode located in the groove
is higher than the average density of the piezoelectric substrate. In the
case where the groove angle is less than about 90°, the stop band
can be increased by specifying the average density of the portion, which
is located in the groove, of the IDT electrode to be higher than the
average density of the piezoelectric substrate.

[0015] In another preferred embodiment of the present invention, at least
some portion of the portion of the IDT electrode located in the groove is
made of at least one type of metal selected from the group consisting of
Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of
metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and
Cu.

[0016] In another preferred embodiment of the present invention, the IDT
electrode preferably includes a laminate of a plurality of electrode
layers, and a resistivity of at least one layer of the plurality of
electrode layers is about 5 μΩcm or less, for example. As a
result, the insertion loss can be further reduced because the resistance
of the IDT electrode can be reduced.

[0017] In another preferred embodiment of the present invention, the
electrode layer having a resistivity of about 5 μΩcm or less is
made of at least one type of metal selected from the group consisting of
Al, Cu, Au, and Ag or an alloy containing at least one type of metal
selected from the group consisting of Al, Cu, Au, and Ag.

[0018] In another preferred embodiment of the present invention, the IDT
electrode preferably includes a laminate of a plurality of electrode
layers, and a diffusion preventing film is disposed in at least one of a
location between the IDT electrode and the bottom of the groove and a
location between the electrode layers adjacent to each other. According
to this configuration, diffusion of an electrode material between the
electrode layers can be prevented. Furthermore, the adhesion between the
electrode layers adjacent to each other can be enhanced.

[0019] In another preferred embodiment of the present invention, the
diffusion preventing film is made of at least one type of metal selected
from the group consisting of Ti, Ni, Cr, and Ta or an alloy containing at
least one type of metal selected from the group consisting of Ti, Ni, Cr,
and Ta.

[0020] In another preferred embodiment of the present invention, the
piezoelectric substrate is made of LiTaO3, for example.

[0021] In another preferred embodiment of the present invention, the IDT
electrode includes a first electrode layer, which is located in the
groove of the piezoelectric substrate and which contains Pt, and a second
electrode layer, which is located outside the groove of the piezoelectric
substrate and which contains Al, the first dielectric layer is made of
silicon oxide, and θ of the Euler Angles (φ,θ,φ) and
the groove angle γ are within the range specified in Tables 1 to 4
below and each of φ and φ of the Euler Angles is within the range
of 0°±5°, where the Euler Angles of the piezoelectric
substrate are specified to be (φ,θ,φ) and the groove angle
is specified to be γ. According to this configuration, in the case
where the piezoelectric substrate is made of LiTaO3, the stop band
can be further increased.

[0022] In another preferred embodiment of the present invention, the
piezoelectric substrate is made of LiNbO3, for example.

[0023] In another preferred embodiment of the present invention, the
following relationships -5°≦φ≦5°,
+80≦θ≦+130°,
-10°≦φ≦+10°, and
10°≦γ<90° are satisfied, where the Euler
Angles of the piezoelectric substrate are specified to be
(φ,θ,φ) and the groove angle is specified to be γ.
Regarding this configuration, in the case where the piezoelectric
substrate is made of LiNbO3 and a boundary acoustic wave in a SH
(Shear Horizontal) mode is utilized, the stop band can be further
increased.

[0024] In another preferred embodiment of the present invention, the
following relationships -5°≦φ≦+5°,
+200°≦θ≦+250°,
-10°≦φ≦+10°, and
10°≦γ<90° are satisfied, where the Euler
Angles of the piezoelectric substrate are specified to be
(φ,θ,φ) and the groove angle is specified to be γ.
Regarding this configuration, in the case where the piezoelectric
substrate is made of LiNbO3 and a boundary acoustic wave in a
Stoneley mode is utilized, the stop band can be further increased.

[0025] In another preferred embodiment of the present invention, the
groove angle is preferably within the range of about 10° or more
and about 80° or less. Regarding this configuration, the acoustic
velocity can be further increased.

[0026] According to various preferred embodiments of the present
invention, a boundary acoustic wave device including a piezoelectric
substrate, a first dielectric layer disposed on the piezoelectric
substrate, and an IDT electrode disposed at a boundary between the
piezoelectric substrate and the first dielectric layer, a groove angle of
a groove in the piezoelectric substrate, in which at least a portion of
the IDT electrode is embedded, is preferably less than about 90 degrees
and, thereby, the acoustic velocity can be further increased.

[0027] The above and other elements, features, steps, characteristics and
advantages of the present invention will become more apparent from the
following detailed description of the preferred embodiments with
reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic plan view of a boundary acoustic wave device
according to a preferred embodiment of the present invention.

[0029]FIG. 2 is a schematic cross-sectional view of a boundary acoustic
wave device.

[0030]FIG. 3 is a graph showing the relationship between the groove angle
γ and the acoustic velocity of a boundary acoustic wave in the case
where an IDT electrode is made of Al.

[0031] FIG. 4 is a graph showing the relationship between the groove angle
γ and the acoustic velocity of a boundary acoustic wave in the case
where an IDT electrode is made of Pt.

[0032]FIG. 5 is a graph showing the relationship between the groove angle
γ and the stop band in the case where an IDT electrode is made of
Al.

[0033]FIG. 6 is a graph showing the relationship between the groove angle
γ and the stop band in the case where an IDT electrode is made of
Pt.

[0034]FIG. 7 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a first modified preferred embodiment of the
present invention.

[0035] FIG. 8 is a graph showing the relationship between the groove angle
γ and the stop band, where the film thickness of a first electrode
layer normalized by the wave length is about 1%, the film thickness of a
portion, which is located in a groove 10a, of a second electrode layer
normalized by the wave length is about 5%, and the film thickness of a
portion, which is located outside the groove 10a, of the second electrode
layer normalized by the wave length is about 10%.

[0036]FIG. 9 is a graph showing the relationship between the groove angle
γ and the stop band, where the film thickness of a first electrode
layer normalized by the wave length is about 3%, the film thickness of a
portion, which is located in a groove 10a, of a second electrode layer
normalized by the wave length is about 3%, and the film thickness of a
portion, which is located outside the groove 10a, of the second electrode
layer normalized by the wave length is about 10%.

[0037]FIG. 10 is a graph showing the relationship between the groove
angle γ and the stop band, where the film thickness of a first
electrode layer normalized by the wave length is about 5%, the film
thickness of a portion, which is located in a groove 10a, of a second
electrode layer normalized by the wave length is about 1%, and the film
thickness of a portion, which is located outside the groove 10a, of the
second electrode layer normalized by the wave length is about 10%.

[0038]FIG. 11 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a second modified preferred embodiment of the
present invention.

[0039]FIG. 12 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a third modified preferred embodiment of the
present invention.

[0040]FIG. 13 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a fourth modified preferred embodiment of the
present invention.

[0041] FIG. 14 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a fifth modified preferred embodiment of the
present invention.

[0042]FIG. 15 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a sixth modified preferred embodiment of the
present invention.

[0043] FIG. 16 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a seventh modified preferred embodiment of the
present invention.

[0044] FIG. 17 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in an eighth modified preferred embodiment of the
present invention.

[0045] FIG. 18 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0046]FIG. 19 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0047] FIG. 20 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0048]FIG. 21 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0049]FIG. 22 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0050]FIG. 23 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0051] FIG. 24 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0052]FIG. 25 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0053] FIG. 26 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0054] FIG. 27 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0055]FIG. 28 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0056] FIG. 29 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0057]FIG. 30 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0058]FIG. 31 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0059]FIG. 32 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0060]FIG. 33 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0061]FIG. 34 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0062]FIG. 35 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0°) is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0063]FIG. 36 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0064]FIG. 37 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 20%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0065]FIG. 38 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0066]FIG. 39 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0067]FIG. 40 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment, where a LiTaO3 substrate having Euler Angles of
(0°,126°,0° is used as the piezoelectric substrate,
the film thickness of Pt normalized by the wave length is about 6%, the
film thickness of Al normalized by the wave length is about 5%, about
10%, or about 15%, the film thickness of SiO2 normalized by the wave
length is about 40%, the film thickness of SiN normalized by the wave
length is about 100%, and the film thickness of Ti between the individual
layers normalized by the wave length is about 10%.

[0068]FIG. 41 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0069]FIG. 42 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0070]FIG. 43 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0071] FIG. 44 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0072]FIG. 45 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0073]FIG. 46 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0074] FIG. 47 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0075]FIG. 48 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0076]FIG. 49 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0077]FIG. 50 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0078]FIG. 51 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment, where a LiTaO3 substrate having Euler Angles of
(0°,138°,0° is used as the piezoelectric substrate,
the film thickness of Pt normalized by the wave length is about 4%, the
film thickness of Al normalized by the wave length is about 5%, about
10%, or about 15%, the film thickness of SiO2 normalized by the wave
length is about 40%, the film thickness of SiN normalized by the wave
length is about 100%, and the film thickness of Ti between the individual
layers normalized by the wave length is about 10%.

[0079]FIG. 52 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of SiO2
normalized by the wave length is about 40%, the film thickness of SiN
normalized by the wave length is about 100%, and the film thickness of Ti
between the individual layers normalized by the wave length is about 10%.

[0080]FIG. 53 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0081]FIG. 54 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0082]FIG. 55 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0083]FIG. 56 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0084] FIG. 57 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 40%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0085]FIG. 58 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0086]FIG. 59 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0087]FIG. 60 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0088]FIG. 61 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,126°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0089]FIG. 62 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0090]FIG. 63 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0°) is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0091]FIG. 64 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0°) is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0092] FIG. 65 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,130°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0093]FIG. 66 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0094] FIG. 67 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment, where a LiTaO3 substrate having Euler Angles of
(0°,134°,0° is used as the piezoelectric substrate,
the film thickness of Pt normalized by the wave length is 4%, the film
thickness of Al normalized by the wave length is 5%, 10%, or 15%, the
film thickness of SiO2 normalized by the wave length is 60%, the
film thickness of SiN normalized by the wave length is 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0095]FIG. 68 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0096]FIG. 69 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,134°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0097]FIG. 70 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 2%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0098]FIG. 71 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0099] FIG. 72 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0100] FIG. 73 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,138°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0101] FIG. 74 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment, where a LiTaO3 substrate having Euler Angles of
(0°,142°,0° is used as the piezoelectric substrate,
the film thickness of Pt normalized by the wave length is about 2%, the
film thickness of Al normalized by the wave length is about 5%, about
10%, or about 15%, the film thickness of SiO2 normalized by the wave
length is about 60%, the film thickness of SiN normalized by the wave
length is about 100%, and the film thickness of Ti between the individual
layers normalized by the wave length is about 10%.

[0102]FIG. 75 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 4%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0103] FIG. 76 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 6%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0104] FIG. 77 is a graph showing the relationship between the groove
angle γ and the stop band in the eighth modified preferred
embodiment of the present invention, where a LiTaO3 substrate having
Euler Angles of (0°,142°,0° is used as the
piezoelectric substrate, the film thickness of Pt normalized by the wave
length is about 8%, the film thickness of Al normalized by the wave
length is about 5%, about 10%, or about 15%, the film thickness of
SiO2 normalized by the wave length is about 60%, the film thickness
of SiN normalized by the wave length is about 100%, and the film
thickness of Ti between the individual layers normalized by the wave
length is about 10%.

[0105] FIG. 78 is a magnified schematic cross-sectional view of a portion
of an IDT electrode of a boundary acoustic wave device described in WO
2008/044411 A1.

[0106]FIG. 79 is a magnified schematic cross-sectional view of a portion
of an IDT electrode in a ninth modified preferred embodiment of the
present invention.

[0107] FIG. 80 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,85°,0).

[0108]FIG. 81 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,95°,0).

[0109]FIG. 82 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,105°,0).

[0110]FIG. 83 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,115°,0).

[0111] FIG. 84 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,125°,0).

[0112]FIG. 85 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,205°,0).

[0113] FIG. 86 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,215°,0).

[0114]FIG. 87 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,225°,0).

[0115] FIG. 88 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,235°,0).

[0116]FIG. 89 shows the relationship between the groove angle (γ)
and the stop band, where the cross-sectional shape is as shown in FIG. 17
and the piezoelectric substrate is formed from a LiNbO3 substrate
having Euler Angles of (0,245°,0).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0117] The present invention will be made clear by explaining preferred
embodiments below with reference to drawings.

[0118]FIG. 1 is a schematic plan view of a boundary acoustic wave device
according to the present preferred embodiment. FIG. 2 is a schematic
cross-sectional view of the boundary acoustic wave device according to
the present preferred embodiment. As shown in FIG. 2, a boundary acoustic
wave device 1 preferably is a so-called three-media boundary acoustic
wave device and is provided with a piezoelectric substrate 10 and first
and second dielectric layers 11 and 12.

[0119] The piezoelectric substrate 10 is not specifically limited insofar
as it is formed from a piezoelectric material. The piezoelectric
substrate 10 can be made of, for example, a LiNbO3 substrate or a
LiTaO3 substrate.

[0120] A first dielectric layer 11 is disposed on the piezoelectric
substrate 10. A second dielectric layer 12 is disposed on the first
dielectric layer 11. The acoustic velocity of the second dielectric layer
12 is larger than the acoustic velocity of the first dielectric layer 11.

[0121] The materials for the first and second dielectric layers 11 and 12
are not specifically limited insofar as the acoustic velocity of the
second dielectric layer 12 is larger than the acoustic velocity of the
first dielectric layer 11. For example, the first and second dielectric
layers 11 and 12 can be made of aluminum nitride, e.g., AlN, besides
silicon oxides, e.g., SiO2, silicon nitrides, e.g., SiN, and the
like.

[0122] More specifically, for example, the first dielectric layer 11 can
be made of silicon oxides, e.g., SiO2, and the second dielectric
layer 12 can be made of a silicon nitride, e.g., SiN, or an aluminum
nitride, e.g., AlN.

[0123] An IDT electrode 13 is disposed at the boundary between the
piezoelectric substrate 10 and the first dielectric layer 11. At least a
portion of the IDT electrodes 13 are located in a plurality of grooves
10a disposed in the piezoelectric substrate 10. That is, at least a
portion of the IDT electrodes 13 are embedded in a plurality of grooves
10a disposed in the piezoelectric substrate 10. Specifically, in the
present preferred embodiment, the whole IDT electrode 13 is embedded in
the groove 10a. The surface of the IDT electrode 13 is preferably flush
with the surface 10b of the piezoelectric substrate 10.

[0124] As shown in FIG. 1, in the present preferred embodiment, the IDT
electrode 13 includes first to third IDT electrodes 13A, 13B, and 13C,
each preferably defined by a pair of comb-shaped electrodes which are
interdigitated with each other. The first to the third IDT electrodes
13A, 13B, and 13C are arranged along the propagation direction of the
boundary acoustic wave. Grating reflectors 14 and 15 are disposed on both
sides of the first to the third IDT electrodes 13A, 13B, and 13C in the
propagation direction of the boundary acoustic wave. These grating
reflectors 14 and 15 are also embedded in the groove 10a disposed in the
piezoelectric substrate 10.

[0125] As shown in FIG. 2, the cross-sectional shape of the groove 10a, in
which the IDT electrode 13 is embedded, is specified to be a shape having
a width which decreases with decreasing away from the surface 10b of the
piezoelectric substrate 10. In the present preferred embodiment, the
cross-sectional shape of the groove 10a is preferably nearly trapezoidal.
In this regard, among the angles formed by an upper end portion, which is
located on the surface 10b side of the piezoelectric substrate 10, of the
inside surface of the groove 10a with the surface 10b of the
piezoelectric substrate 10, the size of an angle (groove angle) γ
located on the side inside the groove 10a is specified to be less than
about 90 degrees, for example. Consequently, the acoustic velocity of the
boundary acoustic wave generated in the IDT electrode 13 is increased, as
described below.

[0126]FIG. 3 is a graph showing the relationship between the groove angle
γ and the acoustic velocity of a boundary acoustic wave in the case
where the IDT electrode 13 is made of Al. As is clear from the results
shown in FIG. 3, the acoustic velocity of the boundary acoustic wave can
be increased as compared with that in the case where the groove angle is
about 90° by setting the groove angle γ to be less than
about 90°. Furthermore, it is clear that in the case where the IDT
electrode 13 disposed in the groove 10a is made of Al having a low
density, the acoustic velocity of the boundary acoustic wave increases
linear functionally as the groove angle γ decreases.

[0127] FIG. 4 is a graph showing the relationship between the groove angle
γ and the acoustic velocity of a boundary acoustic wave in the case
where the IDT electrode 13 is preferably made of Pt. As is clear from the
results shown in FIG. 4, in the case where the IDT electrode 13 is made
of Pt as well, the acoustic velocity of the boundary acoustic wave can
also be increased as compared with that in the case where the groove
angle is about 90° by setting the groove angle γ to be less
than about 90°. However, it is clear that in the case where the
IDT electrode 13 disposed in the groove 10a is made of Pt having a high
density, the rate of change in acoustic velocity of the boundary acoustic
wave relative to a decrease in groove angle γ tends to increase as
the groove angle γ decreases. If the groove angle γ is larger
than about 80°, the acoustic velocity of the boundary acoustic
wave does not increase significantly as the groove angle γ
decreases. On the other hand, if the groove angle γ is about
80° or less, the acoustic velocity of the boundary acoustic wave
increases significantly as the groove angle γ decreases.

[0128] From these results, the acoustic velocity of the boundary acoustic
wave can be increased as compared with that in the case where the groove
angle γ is about 90° by setting the groove angle γ to
be less than about 90° regardless of the type of the IDT electrode
13. In this regard, it is preferable that the groove angle γ is
about 80° or less, for example. The acoustic velocity of the
boundary acoustic wave can be increased significantly regardless of the
type of the IDT electrode 13 by setting the groove angle γ to be
about 80° or less.

[0129] The lower limit of the groove angle γ is not specifically
limited with respect to the relationship with the acoustic velocity of
the boundary acoustic wave. However, the lower limit of the groove angle
γ is, for example, preferably about 10°, preferably about
30°, preferably about 45°, and more preferably about
55°.

[0130] The design parameters of the boundary acoustic wave devices which
exhibit the acoustic velocities of the boundary acoustic wave shown in
FIGS. 3 and 4 are as described below.

[0135] Next, regarding the case shown in FIG. 3 where the IDT electrode 13
is made of Al, the relationship between the groove angle and the stop
band will be described. The results thereof are shown in FIG. 5.
Likewise, regarding the case shown in FIG. 4 where the IDT electrode 13
is made of Pt, the relationship between the groove angle and the stop
band will be described. The results thereof are shown in FIG. 6.

[0136] As shown in FIG. 5, in the case where the IDT electrode 13 is made
of Al having a low density, the stop band tends to become small as the
groove angle γ becomes small. In the case where the IDT electrode
13 is made of Al having a low density, the stop band tends to linear
functionally become small as the groove angle γ becomes small.

[0137] On the other hand, in the case where the IDT electrode 13 is made
of Pt having a high density and the groove angle is less than about
90°, the stop band tends to become larger than that in the case
where the groove angle γ is about 90°.

[0138] As is clear from these results, the stop band can be increased
while the acoustic velocity of the boundary acoustic wave is increased by
specifying the groove angle γ to be less than about 90° and,
in addition, forming the IDT electrode 13 of a high-density, electrically
conductive material, e.g., Pt.

[0139] In this regard, as is clear from the results shown in FIG. 6, in
the case where the IDT electrode 13 is made of Pt having a high density,
the acoustic velocity of the boundary acoustic wave does not linear
functionally increase as the groove angle γ decreases. In the range
of the groove angle γ of about 90° to about 70°, the
stop band tends to increase monotonously as the groove angle γ
decreases, although in the range of the groove angle γ less than
about 70°, the stop band tends to decrease monotonously as the
groove angle γ decreases. However, even in the case where the
groove angle γ is about 55°, the stop band is larger than
that in the case where the groove angle γ is about 90°.
Therefore, it is clear that in the case where the IDT electrode 13 is
made of Pt, in order to increase the stop band, the groove angle γ
is preferably less than about 90° and about 55° or more,
and further preferably about 70°.

[0140] Next, the relationship between the electrode density of the IDT
electrode 13 and the stop band was determined. In each of the case where
the groove angle γ is about 60° and the case where the
groove angle γ is about 90°, when the average density of the
IDT electrode 13 is changed variously, the relationship with the size of
the stop band is shown in Table 5 described below.

[0141] As shown in Table 5 described above, in the case where the average
density of the IDT electrode 13 is smaller than the density (about 7.45
g/cm3) of the piezoelectric substrate 10 (LiTaO3 substrate),
the stop band in the case where the groove angle γ was about
90° was larger than that in the case where the groove angle
γ was about 60°. On the other hand, in the case where the
average density of the IDT electrode 13 is larger than the density (about
7.45 g/cm3) of the piezoelectric substrate 10, the stop band in the
case where the groove angle γ was about 60° was larger than
that in the case where the groove angle γ was about 90°. As
is clear from these results, in the case where the IDT electrode 13 is
embedded in the groove 10a completely and the surface of the IDT
electrode 13 is flush with the surface 10b of the piezoelectric substrate
10, the effect that the stop band is increased by reducing the groove
angle γ is obtained when the average density of the IDT electrode
13 is larger than the average density of the piezoelectric substrate 10.
That is, it is clear that the stop band can be increased while the
acoustic velocity of the boundary acoustic wave is increased by making
the average density of the IDT electrode 13 larger than the average
density of the piezoelectric substrate 10 and, in addition, specifying
the groove angle γ to be less than about 90°.

[0142] Therefore, the material for the IDT electrode 13 located in the
groove 10a is not specifically limited insofar as the material is an
electrically conductive material. However, it is preferable that at least
a portion of the IDT electrode 13 is made of a high-density, electrically
conductive material, e.g., one type of metal selected from the group
consisting of Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at
least one type of metal selected from the group consisting of Pt, Au, W,
Ta, Mo, Ni, and Cu.

[0143] The modified preferred embodiments of the above-described preferred
embodiments will be described below. In this regard, in the following
explanations, members having substantially the same functions as the
members in the above-described first preferred embodiment will be
indicated by the same reference numerals as those set forth above and
explanations thereof will be omitted.

First Modified Preferred Embodiment

[0144] In the above-described first preferred embodiment, the example in
which the whole IDT electrode 13 is embedded in the groove 10a and the
IDT electrode 13 includes a single electrically conductive layer, is
explained. However, the present invention is not limited to this
configuration. For example, only a portion of the IDT electrode 13 may be
embedded in the groove 10a and the other portion may be located on the
side upper than the surface 10b of the piezoelectric substrate 10.
Furthermore, the IDT electrode 13 may include a laminate of a plurality
of electrically conductive layers.

[0145] In the present modified preferred embodiment, as shown in FIG. 7,
the IDT electrode 13 preferably includes an electrode layer laminate of a
first electrode layer 13a, which is disposed on the piezoelectric
substrate 10 in such a way that at least a portion thereof is located in
the groove 10a, and a second electrode layer 13b, which is laminated on
the first electrode layer 13a. A portion of the IDT electrode 13 is
located on the side upper than the surface 10b of the piezoelectric
substrate 10. More specifically, the first electrode layer 13a is
disposed in the groove 10a. Then, a portion of the second electrode layer
13b is located in the groove 10a, and the remainder portion is located on
the side upper than the surface 10b of the piezoelectric substrate 10.

[0146] Alternatively, as shown in FIG. 79, a portion 13Y, which is located
outside the groove 10a, of the IDT electrode 13 may taper with decreasing
distance away from the piezoelectric substrate 10. In the example shown
in FIG. 79, the cross-sectional shape of the portion 13Y, which is
located outside the groove 10a, of the IDT electrode 13 preferably has a
nearly trapezoidal shape in which the length T of the upper base is
smaller than the length R of the lower base.

[0147] As shown in FIG. 79, the portion 13Y, which is located outside the
groove 10a, of the IDT electrode 13 is specified to have a tapered shape
and, thereby, a gap is not formed easily between the first dielectric
layer 11 and the IDT electrode 13. Therefore, scattering of a boundary
acoustic wave due to formation of a gap between the first dielectric
layer 11 and the IDT electrode 13 can be suppressed. As a result,
degradation in characteristics, e.g., an insertion loss, can be
suppressed.

[0148] Meanwhile, in the case where the first dielectric layer 11 is made
of silicon oxide, degradation in temperature characteristics of frequency
due to formation of a gap between the first dielectric layer 11 and the
IDT electrode 13 can also be suppressed.

[0149] In this regard, the cross-sectional shape of the portion 13Y, which
is located outside the groove 10a, of the IDT electrode 13 is not limited
to the nearly trapezoidal shape and may be a semi-elliptic shape, a
semi-oval shape, a triangular shape, or the like.

[0150] The first electrode layer 13a is made of a material, e.g., at least
one type of metal selected from the group consisting of Pt, Au, W, Ta,
Mo, Ni, and Cu or an alloy containing at least one type of metal selected
from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu, having a
density higher than the piezoelectric substrate 10. Furthermore, the
average density of a portion 13Z, which is located in the groove 10a, of
the IDT electrode 13 is specified to become higher than the average
density of the piezoelectric substrate 10. That is, the average density
of the first electrode layer 13a and the portion, which is located in the
groove 10a, of the second electrode layer 13b is specified to become
higher than the average density of the piezoelectric substrate 10.
Concretely, in the present preferred embodiment, the first electrode
layer is made of Pt, and the second electrode layer is made of Al.

[0151] Table 6 described below shows the average density of the portion
13Z, which is located in the groove 10a, of the IDT electrode 13, where
the ratio of the thickness of the first electrode layer 13a to the
thickness of the portion, which is located in the groove 10a, of the
second electrode layer 13b is changed variously.

[0152] Moreover, FIG. 8 shows the relationship between the groove angle
γ and the stop band, where the film thickness of the first
electrode layer 13a normalized by the wave length is 1%, the film
thickness of the portion, which is located in the groove 10a, of the
second electrode layer 13b normalized by the wave length is 5%, and the
film thickness of the portion, which is located outside the groove 10a,
of the second electrode layer 13b normalized by the wave length is 10%.

[0153]FIG. 9 shows the relationship between the groove angle γ and
the stop band, where the film thickness of the first electrode layer 13a
normalized by the wave length is 3%, the film thickness of the portion,
which is located in the groove 10a, of the second electrode layer 13b
normalized by the wave length is 3%, and the film thickness of the
portion, which is located outside the groove 10a, of the second electrode
layer 13b normalized by the wave length is 10%.

[0154]FIG. 10 shows the relationship between the groove angle γ and
the stop band, where the film thickness of the first electrode layer 13a
normalized by the wave length is 5%, the film thickness of the portion,
which is located in the groove 10a, of the second electrode layer 13b
normalized by the wave length is 1%, and the film thickness of the
portion, which is located outside the groove 10a, of the second electrode
layer 13b normalized by the wave length is 10%.

[0155] In this regard, in FIG. 8 to FIG. 10, the graph indicated by
"134°" is the graph in the case where the LiTaO3 substrate having
rotation angles of (0°,134°,0° is used as the
piezoelectric substrate 10. The graph indicated by "138°" is the
graph in the case where the LiTaO3 substrate having rotation angles of
(0°,138°,0° is used as the piezoelectric substrate
10. The graph indicated by "142°" is the graph in the case where
the LiTaO3 substrate having rotation angles of
(0°,142°,0° is used as the piezoelectric substrate
10.

[0156] As shown in Table 6 described above, in the case where the film
thickness of the first electrode layer 13a normalized by the wave length
is 1% and the film thickness of the portion, which is located in the
groove 10a, of the second electrode layer 13b normalized by the wave
length is 5%, the average density of the portion, which is located in the
groove 10a, of the IDT electrode 13 is 5.41 g/cm3 and is smaller
than the density (7.45 g/cm3) of the piezoelectric substrate 10
(LiTaO3 substrate). In this case, as shown in FIG. 8, the stop band
is the largest when the groove angle γ is 90°, and the stop
band tends to become small as the groove angle γ becomes small from
90°.

[0157] As shown in Table 6 described above, in the case where the film
thickness of the first electrode layer 13a normalized by the wave length
is 3% and the film thickness of the portion, which is located in the
groove 10a, of the second electrode layer 13b normalized by the wave
length is 3%, the average density of the portion, which is located in the
groove 10a, of the IDT electrode 13 is 11.34 g/cm3 and is larger
than the density (7.45 g/cm3) of the piezoelectric substrate 10
(LiTaO3 substrate). Likewise, in the case where the film thickness
of the first electrode layer 13a normalized by the wave length is 5% and
the film thickness of the portion, which is located in the groove 10a, of
the second electrode layer 13b normalized by the wave length is 1%, the
average density of the portion, which is located in the groove 10a, of
the IDT electrode 13 is 17.95 g/cm3 and is larger than the density
(7.45 g/cm3) of the piezoelectric substrate 10 (LiTaO3
substrate). In these cases, as shown in FIG. 9 and FIG. 10, it is clear
that the stop band can be made larger than the stop band in the case
where the groove angle γ is specified to be 90° by
specifying the groove angle γ to be less than 90°.

[0158] As is clear from these results, in the case where the IDT electrode
13 is formed from the electrically conductive layer laminate as well, the
stop band can be increased while the acoustic velocity of the boundary
acoustic wave is increased by making the average density of the portion
13Z, which is located in the groove 10a, of the IDT electrode 13 larger
than the average density of the piezoelectric substrate 10. Furthermore,
as is also clear, the effect that the stop band can be increased while
the acoustic velocity of the boundary acoustic wave is increased by
making the average density of the portion 13Z, which is located in the
groove 10a, of the IDT electrode 13 larger than the average density of
the piezoelectric substrate 10 is obtained likewise in the case where
only a part of the IDT electrode 13 is located in the groove 10a and the
other portion is located on the side upper than the surface 10b of the
piezoelectric substrate 10.

[0159] In this regard, the material for the second electrode layer 13b is
not specifically limited insofar as the material is an electrically
conductive material. The material for the second electrode layer 13b may
have a density higher than the density of the piezoelectric substrate 10
or be lower than that. For example, the second electrode layer 13b may be
made of a material, e.g., at least one type of metal selected from the
group consisting of Al, Ag, Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy
containing at least one type of metal selected from the group consisting
of Al, Ag, Pt, Au, W, Ta, Mo, Ni, and Cu, having a density higher than
that of the piezoelectric substrate 10.

[0160] However, if the electrical resistivity of the IDT electrode 13
increases, the insertion loss of the boundary acoustic wave device
becomes large. Therefore, it is preferable that the second electrode
layer 13b is made of a metal or an alloy having a low electrical
resistivity. The electrical resistivity of the second electrode layer 13b
is preferably 5 μΩcm or less. Consequently, it is preferable
that the second electrode layer 13b is made of a low-resistivity
material, e.g., at least one type of metal selected from the group
consisting of Al, Cu, Au, and Ag or an alloy containing at least one type
of metal selected from the group consisting of Al, Cu, Au, and Ag.

[0161] Next, regarding the structure having a cross-sectional shape shown
in FIG. 17, the relationships among θ of the Euler Angles
(φ,θ,φ) of the piezoelectric substrate 10, the groove angle
γ, and the stop band were examined, where the piezoelectric
substrate 10 was made of LiTaO3.

[0162] As shown in FIG. 17, regarding the boundary acoustic wave device
produced in the present experiment, the IDT electrode 13 was formed from
a laminate in which a first diffusion preventing film 13c, a first
electrode layer 13a, a second diffusion preventing film 13d, a second
electrode layer 13b, and a third diffusion preventing film 13e were
laminated in that order from the piezoelectric substrate 10 side. Each of
the first to the third diffusion preventing films 13c to 13e was made of
a Ti film having a film thickness normalized by the wave length of 0.5%.
The first electrode layer 13a was made of a Pt film having a film
thickness normalized by the wave length of 2%, 4%, 6%, or 8%. The second
electrode layer 13b was made of an Al film having a film thickness
normalized by the wave length of 5%, 10%, or 15%. In this regard, the
first diffusion preventing film 13c and the first electrode layer 13a
were located in the groove 10a, and the other portions were located
outside the groove 10a. The first dielectric layer 11 was made of a
SiO2 film having a film thickness normalized by the wave length of
20%, 40%, or 60%, and the second dielectric film 12 was made of a SiN
film having a film thickness normalized by the wave length of 100%.

[0163] FIG. 18 to FIG. 77 show the relationship between the groove angle
γ and the stop band, where the piezoelectric substrate was made of
a LiTaO3 substrate having Euler Angles of (0°,126° to
142°,0°), the film thickness of Pt normalized by the wave
length was 2%, 4%, 6%, or 8%, the film thickness of Al normalized by the
wave length was 5%, 10%, or 15%, and the film thickness of SiO2
normalized by the wave length was 20%, 40%, or 60%.

[0164] Moreover, approximate expressions of the data under the individual
conditions shown in FIG. 18 to FIG. 77 were calculated by using the
method of least squares. In this regard, the approximate expression was
assumed to be a quadratic function (y=ax2±bx+c, where y
represents a stop band and x represents a groove angle). The values of a,
b, and c in the calculated approximate expressions of the data under the
individual conditions are shown in Tables 7 to 11 described below.

[0165] Furthermore, on the basis of the resulting approximate expression,
the size of a stop band when the groove angle was 90° and the
lower limit value of the groove angle of the region in which the stop
band was larger than or equal to the stop band when the groove angle was
90°, that is, the groove angle at which the stop band was equal to
the stop band when the groove angle was 90° was calculated. The
results thereof are also shown in Table 7 to Table 11 described below.

[0166] Next, regarding the case where the piezoelectric substrate 10 was
made of a LiTaO3 substrate, the range of the groove angle, in which
the stop band was able to be made larger than the stop band when the
groove angle was 90°, was calculated from the results shown in
Table 7 to Table 11 and the range of the groove angles which were able to
be formed physically. The calculation results are shown in Tables 12 to
15 described below.

[0167] Concretely, the lower limit of the groove angle in which the
cross-sectional shape of the groove was trapezoidal was about 10°,
where the depth of the groove normalized by the wave length was 2% and
the duty was 0.4 to 0.6. Consequently, for example, in the case where the
lower limit value of the groove angle of the region in which the stop
band was larger than or equal to the stop band when the groove angle was
90° was larger than 10°, the lower limit value of the
groove angle of the region in which the stop band was larger than or
equal to the stop band when the groove angle was 90° was adopted
as the lower limit value of the range of the groove angle in which the
stop band was able to become larger than the stop band when the groove
angle was 90°. Meanwhile, in the case where the lower limit value
of the groove angle of the region in which the stop band was larger than
or equal to the stop band when the groove angle was 90° was less
than 10°, the lower limit value of the range of the groove angle
in which the stop band was able to become larger than the stop band when
the groove angle was 90° was specified to be 10°.

[0168] As is clear from the above description, in the case where the
piezoelectric substrate 10 is made of the LiTaO3 substrate, the stop
band can be increased by specifying θ of the Euler Angles
(φ,θ,φ) and the groove angle γ to be within the range
stipulated in Tables 12 to 15 described below.

[0169] In this regard, each of φ and φ of the above-described data
is specified to be 0°, and it is well known to a person skilled in
the art that the data with respect to 0° can be applied to the
range of 0°±5° in general.

[0170] Meanwhile, in the case where the piezoelectric substrate 10 is
LiNbO3, it is preferable that
-5°≦φ≦+5°,
+80°≦θ≦+130°,
-10°≦φ≦+10°, and
10°≦γ<90° are satisfied, where the Euler
Angles of the piezoelectric substrate are specified to be
(φ,θ,φ) and the groove angle is specified to be γ.
According to this configuration, in the case where the piezoelectric
substrate 10 is made of LiNbO3 and a boundary acoustic wave in the
SH (Shear Horizontal) mode is utilized, the stop band can be further
increased. Moreover, a propagation loss of the boundary acoustic wave can
be reduced particularly, and an occurrence of unnecessary spurious
response can be suppressed effectively.

[0171] FIG. 80 to FIG. 84 show the relationship between the groove angle
(γ) and the stop band, where the cross-sectional shape is as shown
in FIG. 17 and the piezoelectric substrate is made of LiNbO3. In
this regard, the design parameters of the data shown in FIG. 80 to FIG.
84 are as described below.

[0177] First to third diffusion preventing films 13c to 13e; Ti film (film
thickness normalized by wave length: 0.5%)

[0178] Meanwhile, in the case where the piezoelectric substrate 10 is
LiNbO3, it is preferable that
-5°≦φ≦+5°,
+200°≦θ≦+250°,
-10°≦φ≦+10°, and 10°
γ<90° are satisfied. According to this configuration, in
the case where the piezoelectric substrate 10 is made of LiNbO3 and
a boundary acoustic wave in the Stoneley mode is utilized, the stop band
can be further increased. Moreover, a propagation loss of the boundary
acoustic wave can be reduced particularly, and an occurrence of
unnecessary spurious response can be suppressed effectively.

[0179]FIG. 85 to FIG. 89 show the relationship between the groove angle
(γ) and the stop band, where the cross-sectional shape is as shown
in FIG. 17 and the piezoelectric substrate is made of LiNbO3. In
this regard, the design parameters of the data shown in FIG. 85 to FIG.
89 are as described below.

[0185] First to third diffusion preventing films 13c to 13e; Ti film (film
thickness normalized by wave length: 0.5%)

[0186] In this regard, in the present specification, Euler Angles, a
crystallographic axis, and equivalent Euler Angles refer to the
following.

(Euler Angles)

[0187] In the present specification, as for the Euler Angles
(φ,θ,φ) which express the cutting plane of the substrate
and the propagation direction of the boundary wave, the right-handed
Euler Angles described in a literature, "Danseiha Soshi Gijutu Handobukku
(Acoustic Wave Device Technology Handbook)" (the Japan Society for the
Promotion of Science, Committee for Acoustic Wave Device Technology 150,
First copy, First edition, Issued on Jan. 30, 1991, p. 549) was used.

[0188] That is, for example, regarding the crystallographic axes X, Y, and
Z of LiNbO3, the X axis was turned about the Z axis by a φ turn
counter-clockwise, so as to obtain an Xa axis.

[0189] Next, the Z axis was turned about the Xa axis by a θ turn
counter-clockwise, so as to obtain a Z' axis.

[0190] The cutting plane of the substrate was specified to be the plane
including the Xa axis, where the Z' axis was the normal to the plane.

[0191] Then, the direction of the X' axis obtained by turning the Xa axis
about the Z' axis by a φ turn counter-clockwise was specified to be
the propagation direction of the boundary wave.

(Crystallographic Axis)

[0192] Furthermore, the crystallographic axes X, Y, and Z axes given as
initial values of the Euler Angles are specified to be parallel to the c
axis, the X axis is specified to be parallel to any one of a axes in
three equivalent directions, and the Y axis is specified to be in the
direction of normal to the plane including the X axis and the Z axis.

(Equivalent Euler Angles)

[0193] In this regard, it is essential only that the Euler Angles
(φ,θ,φ) in the present invention are crystallographically
equivalent.

[0194] For example, according to a literature (the Journal of Acoustical
Society of Japan, Vol. 36, No. 3, 1980, p. 140-145), LiNbO3 and
LiTaO3 are crystals belonging to trigonal system 3 m point group
and, therefore, Formula [1] holds.

[0196] It is believed that the natural unidirectionality of PFA, for
example, in the case where the positive direction and the negative
direction of propagation are reversed, is equivalent in practice because
the absolute values are equal, although the sign is changed.

[0197] In this regard, the above-described literature relates to the
surface acoustic wave. However, the symmetry of crystal is treated in the
same manner regarding the boundary wave.

[0198] For example, the boundary wave propagation characteristics of the
Euler Angles (30°,θ,φ) are equivalent to the boundary
wave propagation characteristics of the Euler Angles
(90°,180°-θ,180°-φ).

[0199] Moreover, for example, the boundary wave propagation
characteristics of the Euler Angles (30°,90°,45° are
equivalent to the boundary wave propagation characteristics of the Euler
Angles shown in Table 16.

[0200] In this regard, the material constant of the conductor used for
calculation in the present invention is a value of a polycrystal.
However, regarding crystals, e.g., epitaxial films, as well, the crystal
orientation dependence of the substrate is predominant over the boundary
wave characteristics as compared with the crystal orientation dependence
of the film in itself. Therefore, the boundary wave propagation
characteristics at the same level to the extent that cause no problem in
practice are obtained on the basis of Formula [1].

[0201] In the above-described preferred embodiments, the three-media
boundary acoustic wave device formed from a piezoelectric material, and
the first and the second dielectric layers is explained. However, the
boundary acoustic wave device according to the present invention is not
limited to the three-media boundary acoustic wave device. The boundary
acoustic wave device according to the present invention may be a
two-media boundary acoustic wave device not including the second
dielectric layer. In this regard, in the case where the second dielectric
layer is disposed, an insertion loss can be reduced because of a
waveguide effect and, therefore, it is preferable that the boundary
acoustic wave device according to the present invention is the
three-media boundary acoustic wave device.

[0202] In the present invention, the IDT electrode structure is not
limited to the structures shown in the above-described preferred
embodiment and the first modified preferred embodiment. The IDT electrode
may have, for example, structures as shown in FIG. 11 to FIG. 16.

[0203] In the example shown in FIG. 11, the IDT electrode 13 is formed
from a first diffusion preventing film 13c disposed in a groove 10a on a
piezoelectric substrate 10, a first electrode layer 13a disposed on the
first diffusion preventing film 13c, a second electrode layer 13b
disposed on the first electrode layer 13a, and a second diffusion
preventing film 13d disposed between the first electrode layer 13a and
the second electrode layer 13b. Then, all the first and the second
electrode layers 13a and 13b and the first and the second diffusion
preventing films 13c and 13d are disposed in the groove 10a. As shown in
FIG. 11, diffusion of the electrode material from the electrode layers
13a and 13b can be prevented by disposing the diffusion preventing films
13c and 13d between the electrode layers 13a and 13b adjacent to each
other and between the electrode layer 13a and the piezoelectric substrate
10. Furthermore, the adhesion between the electrode layers 13a and 13b
can be enhanced.

[0204] The material for the diffusion preventing films 13c and 13d is not
specifically limited. For example, the diffusion preventing films 13c and
13d can be made of, for example, at least one type of metal selected from
the group consisting of Ti, Ni, Cr, and Ta or an alloy containing at
least one type of metal selected from the group consisting of Ti, Ni, Cr,
and Ta.

[0205] Alternatively, in the example shown in FIG. 12, only a first
electrode layer 13a is disposed as the electrode layer, and a first
diffusion preventing film 13c is disposed between the first electrode
layer 13a and the piezoelectric substrate 10. A part of the first
electrode layer 13a is located in the groove 10a, and the remainder
portion is located outside the groove 10a.

[0206] Regarding the example shown in FIG. 13, as in the example shown in
FIG. 12, the IDT electrode 13 is formed from a first electrode layer 13a
and a first diffusion preventing film 13c. In the example shown in FIG.
13, the surface of the central portion of the first electrode layer 13a
is flush with the surface 10b of a piezoelectric substrate 10, and a
portion excluding the end portion of the first electrode layer 13a is
located in the groove 10a.

[0207] Regarding the example shown in FIG. 14, as in the example shown in
FIG. 11, the IDT electrode 13 is formed from first and second electrode
layers 13a and 13b and first and second diffusion preventing films 13c
and 13d. In the example shown in FIG. 11, the whole IDT electrode 13 is
located in the groove 10a. However, in the example shown in FIG. 14, a
part of the first electrode layer 13a, the second diffusion preventing
film 13d, and the second electrode layer 13b are located outside the
groove 10a. Consequently, in the example shown in FIG. 14, in the inside
of the groove 10a, only the first electrode layer 13a made of a
high-density electrically conductive material is located, and the second
electrode layer 13b made of a low-density electrically conductive
material is not located.

[0208] Regarding the example shown in FIG. 15 as well, as in the example
shown in FIG. 11 and the example shown in FIG. 14, the IDT electrode 13
is formed from first and second electrode layers 13a and 13b and first
and second diffusion preventing films 13c and 13d. In the example shown
in FIG. 15, only the first electrode layer 13a made of a high-density
electrically conductive material of the first and the second electrode
layers 13a and 13b is located in the groove 10a, and the second electrode
layer 13b is located outside the groove 10a. Concretely, the first
electrode layer 13a and the first and the second diffusion preventing
films 13c and 13d are located in the groove 10a, and the second electrode
layer 13b is located outside the groove 10a.

[0209] Regarding the example shown in FIG. 16 as well, as in the examples
shown in FIGS. 11, 14 and 15, the IDT electrode 13 is formed from first
and second electrode layers 13a and 13b and first and second diffusion
preventing films 13c and 13d. In the example shown in FIG. 16, a part of
each of the first and the second electrode layers 13a and 13b is located
in the groove 10a. That is, a part of the second electrode layer 13b made
of a low-density electrically conductive material is also located in the
groove 10a.

[0210] In this regard, in the examples shown in FIGS. 11 to 16, the case
where only the first and the second electrode layers 13a and 13b are
included as the electrode layers is explained. However, the IDT electrode
13 may include at least three electrode layers.

[0211] Meanwhile, the boundary acoustic wave device according to the
present invention may be, for example, a resonator or a filter device.

[0212] Furthermore, the cross-sectional shape of the groove disposed in
the piezoelectric substrate is not specifically limited to the
trapezoidal shape and may be a semi-elliptic shape, a semi-oval shape, a
triangular shape, or the like.

[0213] Moreover, it is essential only that the angle formed by the upper
end portion of the inside surface of the groove with the surface of the
piezoelectric substrate is less than 90 degrees, and a portion which
forms an angle of 90° or more with the surface of the
piezoelectric substrate may be present as a part of the inside surface of
the groove.

[0214] While preferred embodiments of the present invention have been
described above, it is to be understood that variations and modifications
will be apparent to those skilled in the art without departing from the
scope and spirit of the present invention. The scope of the present
invention, therefore, is to be determined solely by the following claims.

Patent applications by Mari Yaoi, Nagaokakyo-Shi JP

Patent applications by Tetsuya Kimura, Nagaokakyo-Shi JP

Patent applications by MURATA MANUFACTURING CO., LTD.

Patent applications in class Orientation of piezoelectric material

Patent applications in all subclasses Orientation of piezoelectric material